Snoop

Snoop is the open source WPF spying utility created by Pete Blois and now maintained by Team Snoop (Cory Plotts,
Dan Hanan,
Andrei Kashcha, Maciek Rakowski, and Jason Jibben).

It allows you to spy/browse the visual tree of a running WPF application (without the need for a debugger) … and change properties ... amongst other things.

Snoop 2.8.0

The most recent version of Snoop,
Snoop 2.8.0, was released on October 4th, 2012. Go to the download page on
CodePlex to download and learn more about it. Most notably, with this release, Bailey Ling has added a PowerShell scripting tab.

Also, don’t forget about the documentation on Pete Blois’ Snoop
page. It is still useful … but hopefully will be less so once I finish my efforts.

Why Aren’t My Apps Showing Up in the App Chooser?

One question that comes up all the time is the situation where the application you are trying to Snoop, isn't appearing in the application chooser (i.e. the combo box that lists the processes you can Snoop). This is more than likely a situation where
the application you are trying to Snoop is running elevated (as Administrator). In order to Snoop these applications, you will also need to run Snoop elevated (as Administrator).

Silverlight Support

Snoop is not currently able to spy Silverlight applications (maybe some day). In the meantime, if you want to do that, I would point you to Koen Zwikstra's awesome utility,
Silverlight Spy.